Beneficiation of low grade coal



May 18.' 1943 s. E. ERlcKsoN l 2,319,394

BENEFICIATION OF LOW GRADE GOAL y Filed Jan.. 29, 1941 5 SheBhs--Shefl l F/GJ.

BY srfP//f/vf. nwo/nso,

ATTORNEY.

May 18, 1943 FIG. `2.

s. E. RIcKsoN BENEFIGIATION 0F LOW GRADE GOAL Filed Jan. 29. 1941 I /Pu/v ofi/wmf" cof-4L I 3 Sheets-Sheet 2 I 604255 CROS/FRI I I con/asf r/Mcr/a/v I SCREEN NIRS/ZE FZ DTATIOIV May 18 1.943 l s. E. EmcKsoN Y 2,319,394

BENEFIGIATION OF LOW GRADE GOAL Filed Jan. 29, 1941 3 Sheets-Sheet 3 AITORNEYL :I zing, and noat and sink methods.

I' Patented M'aylS, 1.943

,l 2,31*394 UNITED snrr1-=zsv PATENT. lomer:

naNmcrarxoN or now omit coax.

stephen n'nylemn, Springdale, cnn.,nsimr to Chemical Construction rporation, New v York, N. Y., a corporation of Delaware 9, 1941, Seflal N0. 376,448

April 5, 1940 Application January 2 In Brazil This low grade. coal. More particularly the invention relates .to the .recovery of both coal and pyritevalues from a low grade coal composed of good coal, bone coal, slate,` and pyrite. In particular this invention relates to the treatment of low grade coal in which the good coal occurs in nne grains and therefore, requires crushing to a comparatively iine degree in order to liberate the f good coal from the accessory material.

' The flotation of coal using standard notation reagents which are for the most parthydrocarbons such as kerosene accompanied if necessary 'by suitable frothers has been-used on .a rather large scale in the past for reducing the 'ash con'- tent of the coal. cedures have been used to recover the coalvalues from waste slush or culm, such procedures being described in the Crawford and Grine U. S. i

Patent 2,136,074 in which the culm is separated into two or more size fractions and each size floated separately using different flotation pro-l cedures for each of the sizes. The Hedley U. S.

Patent 2,136,34i` describes a process for recovere ing coal values from a slush culm by flotation which comprises flotation of the coal fines fol'- tion tailng. rejecting the nne sizes and then subalow ashcoalconcenirate..

Various gravity separation methods have also been employed in the past for recovering coal values from coal contaminated with high ash material. 'Among such lspecific gravity concentration methods are those such as The primary purposes of the above coal treating processes' were for the purpose of obtaining a clean coal concentrate-having a low ash value and were `not concerned with the recovery of materials other than coal that might be present, as for example the pyrites. While many of these More recently -iiotation pro- 3 Claims.' (Cl. 88--90 invention relates to the benenciation of.. to produce a low' coal suitable for locomotive fuel from this low grade material but ordinary coal vwashing methods on this type coal do not;

fers to any or all sulnde bearing materials occurring in low grade coal.

In accordance with the present invention a coal 'treating process is provided which is particularly useful for the beneilciation of low grade coals containing pyrite.v The flow sheet employed in the present invention results in the recovery of a clean coal product having a relatively low ash content and also the recovery of a pyrite product suitable for acid manufacture.

f lowed by screening or classification of the otac In carrying out the present` invention a lowgrade coal containing good coal, bone coal, siate,

andvpyrite is subjected to a crushing operation'` and 'the crushed coall is subjectedto a gravity concentration process followed by froth notation of the gravity concentration tails. The gravity concentrate represents a product having relatively a high percentage of pyrite. The flotation concentrate resulting from ilotationtreatment of the gravity concentration tails produces a clean c'oal concentrate, having a low ash content and 'past procedures -are .commercially successful in obtaining a high grade coal-'concentrate from' certain types of coal, ythey are not at all successful in recoveringthe coal and pyrite values from a low grade coal containing goodcoal, which is present in relatively line-size particles, bone coal,

slate and a relatively high percentage of pyrlte. The beneiiciation of'such low grade coal has been a serious problem in the coal industry heretofore as ythere has been no economical-method for recovering the values therefrom. While the problem is of little economical importancein the United States it is `of very great importancein countries that do not have an abundance of high grade coal such as. for example, Brazil, but do have large amounts of low grade pyrlte containing coal.

une deposits of vthis meson al1-round m' A some time attempts have been made ljBx-azil. For

lhence suitable for fuel.

,The present invention is not concerned with any particular type of notation reagent and it is ian advantage or the invention that it is applicable to the standard reagent combinations. Similarly the invention may be used with various types of flotation equipment.

The invention is also not broadly concerned with the particular type of crushing equipment that is employed to crush the coal. nor in any` particular type of-screen or classier thatmayY be used to e'ect sizing 0f Vthe crushed'coal. The

invention likewiseV is not particularly concernedV with a particular type cfgravity concentrati apparatus which is employed.

The invention will be described in greater de-j tail in conjunction with typical now sheets which have been found to result in good necovery'of clean coal and pyrite products from low grade coals.

Figure l is a diagrammatic now sheet'of al process in which lthe crushed coal is subjected to a jigging operation followed by classincation into a coarse and a fine fraction. `The nne traction is then subjected to flotation resulting in the production of a-clean coal concentrate. The

fraction is subjectedto a gravity concentration' treatment itablinc) to produce a pyrite concenflow sheet of Figure 1, in which a run of mine low grade coalcontaining pyrite, from a Brazilian coal deposit, in which the good coal particles were -35 mesh in size and in which the pyrltewas satisfactorily liberated from attachments by crushing to -l-10 mesh is fed into a suitable crushing circuit which may consist of a coarse jaw crusher followed by a roll-'crusher or rod-mill, if

desirable, which results in the production of a -10 mesh material. The crushed coal is then subjected to a jigging operation which results in the production of a concentrate rich in pyrites.

The jig tails are subjected to a suitable classifying operation to produce a coarse fraction approximately plus 35 mesh which is returned to the crushing circuit and a -35 mesh fraction. This classification may be accomplished by any suitable classifler, preferably, however, a screen is used because of the more desirable size control obtained. The -35 mesh material is then further classified into sands and lines. The sands are subjected to a 'cabling operation producing a pyrite concentrate and dirty coal tails which upon rtreatment by flotation result in the production' of a clean low ash concentrate. The classifier fines are subjected to a direct notation treatment to -produce a clean low ash coal concentrate.

. These froth flotation operations may be carried out in the presence of any suitable collector and frothing reagents such as. for example, fuel oil and an alcohol frother. The amount of reagents and reagent combinations may of course -be varied to obtain best results from each particular size range of feed.

It is to be noted also that the ne fraction may be deslimed by a hydroseparator or the like prior to the froth flotation. The otation concentrate obtained from the course fraction ory sands, if desired, may be subjected .to a screening operation to produce a coal concentrate of higher fuel value. The combined pyrite concentrates from the jigg'ing and tabling 'operations represent a high percentage of pyrites which were present in the run of mine coal feed. This pyrite product is suitable for use in acid manufacture. The combined coal concentrates represent a good recovery of coal which is sufficiently low in ash to be suitable for combustion purposes.

'I'he following example illustrates in greater detail the operation of the present invention in ac cordance' with the flow sheet of Figure 1.

A Brazilian crude coal was crushed to approxi? mately -10 mesh and subjected to a ligging 0P- eration producing a pyrite concentrate and a low grade coaltailing.

'I'hese iig tails were screened on a 35 mesh screen the oversize being returned to the crushing circuit and theundersize further classied trate which was then screened on an approximately 50 mesh screen to produce a low ash coal concentrate.

The fines were subjected to froth flotation to produce a recleaner concentrate of a low ash The conditions under which the flotation operations were carried out are summarized as fol- Rougher notation-(Sands) Coarse .feed (-35 mesh) Procedure Per cent solids 22 Time of fioat minutes 4l/2 Reagents-Lbs/ton flotation feed Kerosene-LOB-conditioned 2 minutes prior to iioat 'Alcohol frorther0.0'7conditioned 2 minutes Prior to float Alcohol frother-O'T-to float Rcugher conc. screened on 50 mesh. No cleaning. Total reagents-Per ton of original run of mine coal Thedata in the following table represent the results obtained in Example l.

Table Product TousY Sulfur Ash Carbon Run o! mine coal 1060 Coarse classified feed (sands). 500 Table concentrate 200 'Table tail 300 Rougher flotation concentrato 257 Rougher flotation tail 03 50 mesh screen oversize. 93 50 mesh screen undcrsize. 144 Fine classified feed (fines). 500 Rougher flotation concentrate 400 4. 29 17. 96 Rougher flotation tail 8. 16 06. l Cleaner flotation concentrate 365 3. 82 14. 8 Cleaner dotation tall 36 9. 43 52. 54 Re-cleaner notation concentrete 345 3. 52 13. 26 lie-cleaner flotation tail 20 8. 66 38. 86 Combined coal concentrate. 438 3. 08 13. 84

WdaM Total Rec rin: Per cent Per cent Pyrite concentrate 20. 0 76. 16 Coal concentrate 43. 8 7 82. 43

- An analysis of the above results show thaty 57.63% of the cogxnbusible material is obtained in agood coal product which has only 13.84% ashpresent and hence entirely satisfactory for combustion purposes. Likewise 76.16% of the suldes are obtained which are suitable forv use inacid manufacture. 4

Results similar to those of Example 1 are obtained when' the present invention is carried out in `accordance with the ow sheets of either Figure 2 or Figure 3', which differ only in detail from the flow sheet of Figure 1.

Referring specifically to the flow sheet of Fis. 2 a run of mine low grade coal containing pyrite is fed into a coarse jaw crusher -thence through a roll-crusher and onto a screen of approximately 10 mesh. The oversize or plus 10 mesh material is returned to roll-crusher. The under-` may be deslimed and the sand floated to pro-l duce a low ash coal concentrate or inmany cases v can be floated directly without desliming. f

Referring now to the flow sheet of Figure 3 the run of mine coal isvcrushed and fed onto a double deck screen 'of approximately 10 and 35 mesh. The -10 plus 35 mesh material is fed to a jig, a pyrite concentrate is produced and a high ash coal tail obtained.- This tail is fura ther crushed and fed onto a 35 mesh screen, the oversize being returned to the crusher. the undersize -35 mesh is combined with the '35 mesh material from the double deck screen and classified into a fine and a coarse fraction. The remaining steps are the same as those outlined in connection with the ne and coarse fractions of Figure 2.

Essentially the three flow sheets illustrated all comprise the steps of crushing the coal subjecting to a 'ligging operation, classifying the jig tails into a coarse and ne fraction, subjecting the coarse fraction to a tabling operation followed by froth notation of the table tails and subjecting the fine fraction to dotation without tabling. Various coals, however, differ in the y degree to which they must be crushed to liberate the coal and pyrite values and hence it is desirable that the crushing and classifying operations -may be varied as indicated inthe flow sheets to obtain the best results.

` which comprises crushing the coal to -10 mesh,

subjecting the crushed coal to a gravity concentration operatioh to produce a pyrite concentrate and a low grade coal tail, classifying the tails into a coarse and a fine fraction, subjecting the-coarse fraction to a gravity concentration operation followed by froth flotation of the coal values from the gravity concentration coarse fraction tails, and recovering thecoal values from the fine fraction vby froth flotation. l

2. A method of'recovering pyrite and coal values from a low grade coal containing pyrite which comprises crushing the coal to -10 mesh, subjecting the crushed coal to a jigging operation to i produce a pyrite concentrate anda low grade coal tail, classifying the tails into a coarse and a fine fraction,.subjecting the coarse fraction to a tabling operation followed by froth flotation of the coal values from the table coarse, fraction tails, and recovering the coal values from the fine fraction by froth flotation.

3. A method of recovering pyrite and coal val-'- ues from a low gradecoal containing pyrite which comprises crushing the coal'to -10 mesh, subjecting the crushed coal to a ligging operation -to produce` a pyrite concentrate and a low grade coal tail, crushing-the tails to -35 ymesh and classifying into a coarse and a ne fraction,

by froth flotation. A

' STEPHEN E. ERICKSON. 

